Donald Savage
Headquarters, Washington, DC April 19, 1995
(Phone: 202/358-1547) EMBARGOED UNTIL: 2:00 PM EDT
Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5566)
Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4514)
RELEASE: 95-53
HUBBLE DISCOVERS NEW DARK SPOT ON NEPTUNE
The distant, blue-green planet Neptune has again surprised
astronomers with the emergence of a new great dark spot in the cloudy
planet's northern hemisphere. The feature was discovered by NASA's Hubble
Space Telescope.
Only last June, Hubble images revealed that a great dark spot in
the southern hemisphere - discovered by the Voyager 2 spacecraft during
its 1989 flyby - had mysteriously disappeared.
The new dark spot is a near mirror-image of the previous feature
first mapped by Voyager 2. The northern dark spot discovered by Hubble is
accompanied by bright, high-altitude clouds. As atmospheric gases flow up
over the spot, they cool to form these methane-ice crystal clouds.
"Hubble is showing us that Neptune has changed radically since
1989," said Heidi Hammel of the Massachusetts Institute of Technology.
"New features like this indicate that with Neptune's extraordinary
dynamics, the planet can look completely different in just a few weeks."
Like its predecessor, the new spot might be a hole in Neptune's
methane cloud tops that gives a peek to lower levels of the atmosphere.
"We weren't surprised the other spot disappeared," said Hammel.
"It was kind of 'floppy' because it changed shape as atmospheric
circulation carried it around the planet." (By contrast, Jupiter's Great
Red Spot, which is similar to Neptune's original spot in relative size and
position, has remained stable in appearance for at least 300 years.)
Hammel points out that studying the dynamics of Neptune's immense
atmosphere might lead to a better understanding of Earth's atmosphere.
"Neptune's unusual behavior is showing us that though we can make great
models of planetary atmospheric circulation, there may be key pieces
missing."
Energy from the Sun drives Earth's weather system. However, the
mechanism must be very different on Neptune because the planet radiates
two times more energy than it receives from the dim, distant Sun.
Neptune's atmosphere might be so dynamic because the cloud tops
are warmed from below by this strong internal heat source. A slight
change in the temperature differential from cloud bottom to top might
trigger rapid, large-scale changes in atmospheric circulation.
Since the 1989 Voyager flyby, astronomers using ground-based
telescopes have not been able to resolve the subtle structures in
Neptune's variable atmosphere, particularly the low-contrast dark
features.
The astronomers don't know how long the new feature will last. For
the first time in planetary history though, Hubble will allow astronomers
to follow the details of Neptune's atmospheric changes over at least a
decade.
The Space Telescope Science Institute is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA) for
NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).
- end -
NOTE TO EDITORS: Images and a video depicting Neptune rotating
are available to media representatives by calling NASA's Broadcast and
Imaging Branch at 202/358-1900. NASA photo numbers are:
Color: B&W:
Neptune 3 visits: 95-HC-189 95-H-193
Neptune Dark Spot: 95-HC-190 95-H-194
Image files in GIF and JPEG format may be accessed via anonymous
ftp from ftp.stsci.edu in /pubinfo:
GIF JPEG
Neptune 3 visits: /pubinfo/gif/Nept3.gif /pubinfo/jpeg/Nept3.jpg
Neptune Dark Spot: /pubinfo/gif/NeptDS.gif /pubinfo/jpeg/NeptDS.jpg
The same images are available via World Wide Web from links in URL
http://www.stsci.edu/pubic.html or more directly from
http://www.stsci.edu/Latest.html